Detailed discussion of broadly regional tectonic features that may have affected the distribution and stratigraphic relations of Upper Cambrian and Lower Ordovician beds in Kansas is not within the scope of this study. The relationship of the formations, however, reveals the geologic history of the older formations in general terms.
The following summary of the depositional history of the Upper Cambrian and Lower Ordovician beds in Kansas is based upon an interpretation of the variations in thickness and distribution of the stratigraphic units composing that part of the geologic section. The variation in thickness and the distribution may in part reflect changing extent of seaways; in part it may be the result of deformation due to tectonic activity and of topographic relief of the land surface upon which the beds were laid down; or it may result from a combination of these.
Tectonic activity may change the composition, texture, thickness, and distribution of clastic sediments by elevating new areas to an altitude at which erosional processes may become effective or by lowering old areas that have been supplying sediments below the altitude where erosion is effective. It may thus bring about environmental changes that are either favorable or unfavorable for the deposition of the nonelastic precipitates, evaporites, and organic deposits.
The composition of clastic sediments is dependent upon the composition of the source rock. The elevation of new areas and consequent exposure to erosional processes may bring about changes in the composition of clastic deposits. The texture of sediments is affected by the competency of transporting agents and by the distance detritus is carried, both of which reflect differences in elevation of the land surface. The total thickness of sediments that may be deposited is determined mainly by the amount of source material available, the effectiveness of the geological processes, and the length of time those processes are effective.
The original distribution of sediments is influenced by the character of land surface. Deposits normally will accumulate in basins and be absent from high areas. The original distribution may be modified by erosion following change in elevation. Sediments tend to be removed or thinned in uplifted areas and to be preserved in depressed areas. The presence or absence of stratigraphic units may therefore be an important key to the interpretation of structure.
Erosion probably has shaped the surface upon which some of the beds have been deposited. Thinner accumulations of sediment generally will extend over high areas and thicker accumulations over low areas. In any case, some form of tectonic activity is necessary to bring about conditions favorable to effective local erosion.
If it is unknown whether the upper or lower part of a sedimentary sequence is missing, it is uncertain whether beds are absent or thin because of nondeposition or because of erosion following deposition.
The relationship and character of stratigraphic units within the Upper Cambrian and Lower Ordovician sequence indicate that a relatively high area of broad extent occupied the central part of Kansas at the beginning of Cambrian deposition. [Note: The absence of the Lamotte beneath the Bonneterre in some wells in central Kansas suggests topographic elevation of the Pre-Cambrian rocks in this area. However, the occurrence of Lamotte sandstone beneath the Bonneterre in the downwarped area of McPherson County (cross section A-A') and the beveling of the pre-Roubidoux surface reveal that the Lamotte was originally more widespread than now. The widespread occurrence of the Bonneterre in north-central Kansas and south-central Nebraska, in many wells that have been drilled since the completion of this report, indicate that the elevation was not high. The only wells in which the Bonneterre does not occur are in areas in which the Roubidoux overlies the beveled surface of the Pre-Cambrian rocks.] Its location in relation to the present more recently formed structural features may be described as including the east and south flank of the Central Kansas uplift and all of the Salina basin.
In Arbuckle time the center of subsidence was in the Ozark region of Missouri, but the western margin of the basin extended into eastern Kansas. The high central part of Kansas may have formed the western boundary of Late Cambrian deposition belonging to the Ozark province. On the other hand, the absence of Upper Cambrian and some Lower Ordovician strata in the central Kansas area may reflect pre-Roubidoux stripping of deposits that once were extensively distributed. A broad basin in the western part of the state probably received deposits that were eastward extensions of the Sawatch quartzite of the Rocky Mountains and the Deadwood formation of the Black Hills.
A relatively high area in western Kansas near the Colorado boundary that extends from Gove County through western Logan County into Kearny County is indicated by absence of Lamotte sandstone, thinness of Bonneterre dolomite, and absence of the Eminence dolomite. Its western margin has not been determined. The Lamotte is present in well 22 in Logan County and well 20 in Trego County, although absent in well 21 in Gove County.
Such structural features as the Central Kansas uplift and the Nemaha anticline from which the upper parts of the Arbuckle sequence are now absent were not formed until later geologic time.
Kansas well samples indicate, as in Missouri (Lee, 1943, p. 104), that four epochs of deposition are to be recognized in Late Cambrian and Early Ordovician time. The successive groups of deposits, which are separated by major unconformities, include the following:
- Unconformable deposition of Lamotte sandstone on the Pre-Cambrian surface, followed by conformable deposition of the Bonneterre dolomite, Davis formation, and Derby and Doe Run dolomites, and closing with the upwarping and erosion of Doe Run and older deposits.
- Deposition of the Potosi, Eminence, and Proctor dolomites. The interruption of sedimentation at the end of Proctor time corresponds to the unconformity between the Cambrian and Ordovician Systems as defined in the upper Mississippi Valley.
- Deposition of the Van Buren formation, including the basal Gunter sandstone member and the Gasconade dolomite. This is followed by a conspicuous unconformity, for the overlying Roubidoux in different places overlies the Pre-Cambrian, Bonneterre, Eminence, and Gasconade. This unconformity is scarcely perceptible in Missouri but is pronounced in Kansas.
- Deposition of the Roubidoux dolomite, Jefferson City dolomite, Cotter dolomite, and possibly the Powell dolomite and Smithville limestone. The interruption of sedimentation at the end of Smithville time corresponds i.o the unconformity at the base of the Chazy group of Early and Middle Ordovician age. In Kansas this unconformity occurs at the base of the St. Peter sandstone.
The distribution and unconformable relationships of these will be discussed in order from oldest to youngest.
First Depositional Cycle, Lamotte to Doe Run
The Lamotte sandstone was laid down on an irregular Pre-Cambrian surface, and accumulation of sediment served to level off many inequalities in the surface. Probably this sedimentation was confined mainly to topographic depressions in eastern and western Kansas.
Deposition of Lamotte sediments gave way without interruption to widespread Bonneterre deposition, overlapping on the Pre-Cambrian surface where it was too high to be covered by Lamotte sandstone. The clastic character of the Bonneterre in some wells, as in Chautauqua, Wilson, and McPherson counties, may be the result of nearness to weathering granite. The Davis formation and the Derby and Doe Run dolomites probably were restricted to the deeper parts of the Ozark basin and were not deposited in Kansas.
The lithologic differences in the Bonneterre in eastern and western Kansas may be due to a facies change. Areas of thick Bonneterre in northern and southern McPherson County and the presence of Roubidoux in the Salina basin indicate more widespread deposition than indicated by areas at present underlain by Bonneterre. The absence of Bonneterre beneath the Roubidoux on structurally high areas in central Kansas has been interpreted by some geologists as indicating an area of nondeposition, but these areas were certainly beveled before the deposition of the Roubidoux and probably earlier. There was no barrier toward the north where the Bonneterre is continuous into western Kansas.
An area of moderate elevation in western Kansas at the beginning of Late Cambrian time is indicated by the absence of Lamotte sandstone and probably lower beds of the Bonneterre from wells in Kearny and Gove counties and in western Logan County (wells 12, 21, and 23), although the Lamotte is present in southeastern Logan County and in Trego County (wells 20 and 22).
The unconformity at the end of the first cycle of deposition is represented by the absence of the Davis formation and the Derby and Doe Run dolomites. Either they were not deposited in Kansas or they were removed by post-Doe Run erosion.
Second Depositional Cycle, Potosi to Eminence
Deposition of the Potosi dolomite, which initiated the second depositional cycle, seemingly was restricted to the deeper parts of the Ozark basin in Missouri. It may have extended into southeastern Kansas although it has not been positively identified there. The Eminence dolomite, which conformably overlies the Potosi dolomite, extended westward and overlapped unconformably onto the Bonneterre dolomite in Kansas. Nowhere in Kansas is the Eminence dolomite known to lie directly on the Pre-Cambrian surface. This indicates either that the Eminence was restricted to eastern and western Kansas and was not deposited upon the areas of uplift that were subsequently beveled by the Roubidoux, or that it was deposited broadly on the eroded surface of the Bonneterre and was removed by subsequent erosion from the crests of uplifted areas. Slight differences in the Eminence in eastern and western Kansas suggest that the rocks of this unit did not extend across the belts of uplifted Pre-Cambrian rocks in the central part of the state, but the occurrence of Eminence in the syncline in southern McPherson County suggests that it was originally more widely distributed than now.
It is not possible to determine the original distribution of the Eminence dolomite or what thickness of beds has been removed. The presence of a thin section of Eminence dolomite in western Logan County indicates that the formation probably was deposited in the extreme western part of the state and that upwarping and erosion at the close of the second depositional cycle removed all the Eminence dolomite from the area represented by wells in Kearny and Gove counties.
Third Depositional Cycle, Van Buren to Gasconade
The third cycle of sedimentation extends from the deposition of the Gunter sandstone member of the Van Buren to the close of Gasconade time. In Missouri, the Van Buren-Gasconade sequence normally overlies the Proctor or Eminence. In Kansas, the sequence (as shown in cross sections A-A' and B-B') bevels the older rocks from the Eminence to the Pre-Cambrian. In southern McPherson County it overlies a thin section of Eminence. The relations are interpreted as indicating the continued growth of broad anticlines trending east of north with beveling of their crests by the Van Buren. In view of the presence of the Eminence beneath the Van Buren in southern McPherson County (well 16) it is presumed that that area was part of a pre-Roubidoux syncline in which the Van Buren-Gasconade sequence and the Eminence and Bonneterre, which were originally more widespread, were preserved although stripped from the crests of the adjacent anticlines. If the Van Buren-Gasconade sequence once overlay the Eminence in the basin of western Kansas, it was removed from that area by pre-Roubidoux erosion.
The Van Buren-Gasconade sequence overlaps unconformably across the beveled edges of the Eminence and Bonneterre dolomites onto the Pre-Cambrian surface in Sumner and Sedgwick counties (cross section A-A'). The coarsely elastic character of the basal beds of the Van Buren in Sedgwick and Sumner counties (wells 6 and 7) is probably due to the nearness of exposed granite.
In Missouri, the Roubidoux formation everywhere overlies Gasconade dolomite. Upper beds of the Gasconade are absent locally in southeast Missouri, and their absence has been explained as resulting from post-Roubidoux solution (Dake, 1930, p. 158). Although the unconformity in Missouri is obscure, the Roubidoux dolomite in Kansas is conspicuously unconformable on the underlying rocks and rests in turn on each of the older formations and on Pre-Cambrian rocks in a considerable area in the central part of the state (Fig. 7).
Fourth Depositional Cycle, Roubidoux to Smithville
The widespread distribution of the Roubidoux, Jefferson City, and Cotter dolomites in Kansas, except where removed by post-Arbuckle erosion, indicates that the greatest westward extension of Ozark deposition probably occurred in the fourth depositional cycle, Roubidoux to Smithville.
In eastern Kansas, the Roubidoux dolomite unconformably overlies the Van Buren-Gasconade sequence and the Bonneterre dolomite. That some areas of the pre-Roubidoux eroded surface retained considerable relief is suggested by the absence of the lower part of the Roubidoux in well 15 (cross section B-B'), where it is only 72 feet thick and overlies an elevated thin body of Bonneterre on the crest of a structural arch. Local variations in the thickness of the Roubidoux occur elsewhere (well 6 of cross section B-B'). Its thickness reaches 350 feet in western Kansas.
In the central part of the state, the Roubidoux unconformably overlies the Pre-Cambrian rocks on structurally high areas, as shown in well 8 of cross section B-B', and on a more well-defined arch farther west in wells 9, 18, and 19 in Rice and Barton counties. Between these structural arches the well in southern McPherson County reveals a relatively deep and sharp syncline across which the Roubidoux overlies the Van Buren-Gasconade sequence and older rocks. In western Kansas the Roubidoux overlies the Eminence in a broad structural basin on the margin of which the Roubidoux overlies Bonneterre (cross sections A-A' and B-B').
The widespread deposition of Jefferson City and Cotter deposits in Kansas followed Roubidoux deposition. Although a minor break between the Jefferson City and Cotter dolomites is recognized in Missouri by some geologists, it has not been identified in Kansas.
The Powell dolomite and Smithville limestone succeeded the Cotter dolomite in parts of Missouri and probably in Kansas with only minor interruptions in sedimentation. Originally they were distributed widely, but if they reached Kansas they were removed from most of the state prior to St. Peter time. That remnants of these beds may survive in southwestern Kansas is indicated by meager samples from wells in Clark, Kiowa, Meade, and Gray counties.
At the close of the fourth cycle of deposition, the beds were elevated in northern Kansas and truncated. Slight northward convergence of beds below the Roubidoux dolomite indicates that some deformation in this direction may have preceded the warping that took place before St. Peter deposition. All the Jefferson City and Cotter deposits and part or all of the Roubidoux dolomite were removed. from northern Kansas during this extensive period of erosion. The Cotter dolomite probably was removed from all but the most southern part of the state. That the northward truncation of beds and overlap of the St. Peter sandstone continued into Nebraska is indicated by the absence of post-Gasconade beds from the Union Stock Yards Company No. 3 well at Omaha, Nebraska, as determined by McCracken of the Missouri Geological Survey (McQueen and Greene, 1938, p. 44).
The high area in western Kansas also seems to have received additional warping at the end of early Ordovician time, as indicated by the removal of all the Jefferson City and Cotter and upper part of the Roubidoux deposits from wells in western Logan County (well 23) and Kearny County (well 12), whereas,these formations are present in wells to the east.
Kansas Geological Survey, Geology
Placed on web Jan. 22, 2010; originally published June 1948.
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